U.S. patent application number 10/713005 was filed with the patent office on 2004-05-20 for method and device for accessing frame memory within display panel driver.
This patent application is currently assigned to NEC PLASMA DISPLAY CORPORATION. Invention is credited to Hashimoto, Katsuyuki, Inoue, Toshiaki.
Application Number | 20040095356 10/713005 |
Document ID | / |
Family ID | 32290227 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040095356 |
Kind Code |
A1 |
Inoue, Toshiaki ; et
al. |
May 20, 2004 |
Method and device for accessing frame memory within display panel
driver
Abstract
A method for accessing a frame memory integrated within a
display panel driver driving a display panel is composed of
serially performing write operations for writing sub-field data of
a pixel line within the display panel for a plurality of sub-fields
into the frame memory, and serially performing read operations for
reading sub-field data of a plurality of pixel lines for a
sub-field from the frame memory. At least two of the write
operations are allowed to be performed between adjacent two of the
read operations.
Inventors: |
Inoue, Toshiaki; (Tokyo,
JP) ; Hashimoto, Katsuyuki; (Tokyo, JP) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
NEC PLASMA DISPLAY
CORPORATION
TOKYO
JP
|
Family ID: |
32290227 |
Appl. No.: |
10/713005 |
Filed: |
November 17, 2003 |
Current U.S.
Class: |
345/531 |
Current CPC
Class: |
G09G 3/288 20130101;
G09G 3/2022 20130101; G06F 3/038 20130101; G09G 5/393 20130101;
G09G 2360/126 20130101 |
Class at
Publication: |
345/531 |
International
Class: |
G09G 005/39 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2002 |
JP |
2002-332949 |
Claims
What is claimed is:
1. A method for accessing a frame memory integrated within a
display panel driver driving a display panel, said method
comprising: serially performing write operations for writing
sub-field data of a pixel line within said display panel for a
plurality of sub-fields into said frame memory; and serially
performing read operations for reading sub-field data of a
plurality of pixel lines for a sub-field from said frame memory,
wherein at least two of said write operations are allowed to be
performed between adjacent two of said read operations.
2. The method according to claim 1, further comprising: providing
first and second horizontal sync signals, wherein said write
operations for writing said sub-field data of said pixel line for
said plurality of sub-fields are performed during a single cycle of
said first horizontal sync signal, and wherein each of said read
operations for reading said sub-field data of said pixel line for
each of said plurality of sub-fields is performed during a single
cycle of said second horizontal sync signal.
3. The method according to claim 1, further comprising: providing a
read request signal activated for requesting said read operations,
and providing a write request signal activated for requesting said
write operations, wherein, in response to activation of said read
request signal, associated one of said read operations is performed
immediately after said activation of said read request signal when
said frame memory is not engaged in write operation, while said
associated one of said read operations is performed after
completion of associated one of said write operations when said
frame memory is engaged in said associated one of said write
operations.
4. The method according to claim 3, wherein said read request
signal is kept activated until said associated one of said read
operations is initiated.
5. The method according to claim 1, further comprising: providing a
read request signal activated for requesting said read operations,
and providing a write request signal activated for requesting said
write operations, wherein, in response to activation of said write
request signal, one of said write operations associated with said
activation is performed immediately after said activation of said
write request signal when said frame memory is not engaged in read
nor write operation, said associated one of said write operations
is performed after completion of associated one of said read
operations when said frame memory is engaged in said associated one
of said read operations, and said associated one of said write
operations is performed after completion of previous one of said
write operations when said frame memory is engaged in said previous
one of said write operations.
6. The method according to claim 5, wherein said write request
signal is kept activated until said associated one of said write
operations is initiated.
7. A memory controller for controlling access to a frame memory
comprising: a timing controller developing read and write start
pulse signals in response to write and read request signals, and a
read/write operation control unit responsive to said read and write
start pulse signals for initiating read operations for reading
sub-field data from said frame memory, and write operations for
write sub-field data into said frame memory, wherein said timing
controller develops said read and write start pulse signals to
allow said read/write operation control unit to initiate at least
two of said write operations between adjacent two of said read
operations.
8. The memory controller according to claim 7, wherein said timing
controller includes: a state machine switching a state of said
frame memory among a plurality of states in response to a reset
signal, said write and read request signals, said plurality of
states comprising: an idle state, a write start state, a first
write operation state, and a second write operation state, wherein
said state machine is designed to switch said state of said frame
memory to said idle state in response to activation of said reset
signal, to switch said state of said frame memory to said write
start state in response to first activation of said write request
signal, to unconditionally switch said state of said frame memory
to said first write operation state after placing said frame memory
in said write start state to initiate one of said write operations,
and to switch said state of said frame memory to said second write
operation state in response to second activation of said write
request signal during said one of said write operations to initiate
next one of said write operations.
9. The memory controller according to claim 8, wherein said
plurality of states further comprising: a read start state, and a
read operation state, wherein said state machine is designed to
switch said state of said read start state in response to
activation of said read request signal when said frame memory is
placed in any of said idle state and said first and second write
operation states, and to unconditionally switch said state of said
frame memory to said read operation state after placing said frame
memory in said read start state to initiate one of said read
operations.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is generally related to a method and
device for accessing a frame memory, particularly, to an accessing
technique of a frame memory integrated within a display panel
driver adopting a sub-field addressing method.
[0003] 2. Description of the Related Art
[0004] The sub-field addressing method is a typical drive sequence
for achieving a gray scale in pixels of a plasma display panel. The
sub-field addressing method divides each frame into a plurality of
sub-fields, and each of the sub-fields is further divided into an
address period and a sustain period. Each pixel is activated or
turned on during the sustain period(s) of one or more selected
sub-fields in response to the intensity thereof, and this selective
activation achieves a gray scale in each pixel. In order to emit
light from a given pixel site during a given sub-field, the pixel
site is selected to receive a write address pulse during the
associated address period, and a sustain voltage is applied to the
selected pixel site to cause an emission of light therefrom during
the associated sustain period.
[0005] FIG. 1 shows a drive sequence to achieve a 16 gray scale
using a sub-field addressing method. The drive sequence divides
each frame into four sub-fields SF1 to SF4. The length of each of
the four sub-fields is different. The first sub-field SF1 has a
sustain period with eight sustain cycles, each corresponding to a
sustain pulse, the second sub-field has four sustain cycles, the
third sub-field has two sustain cycles, and the fourth sub-field
has a sustain period with only one complete sustain cycle. The
pixel site is activated during one or more of the sub-fields SF1 to
SF4 selected in response to the intensity or the gray scale level
of the pixel site to achieve a 16 (=2.sup.4) gray scale. The number
of available gray scale levels increases as an increase in the
number of the sub-fields. In order to achieve a 256 gray scale, a
frame is necessary to include eight sub-fields.
[0006] Implementing a sub-field addressing method requires
appropriate allocation of sub-field data of each sub-field in a
frame memory disposed within a display driver, where the sub-field
data is representative of illumination or extinction of each pixel
during each sub-field. FIGS. 2A to FIGS. 2D illustrates an
exemplary memory map of a frame memory adapted for the sub-field
addressing method. The frame memory stores image data for two
frames to achieve a double buffering technique. This requires the
frame memory to have a memory capacity more than 96 Mbits for
driving a display panel in accordance with the full color WXGA
(wide extended graphics array) specification, which involves
1365.times.768 pixels with a 16 bit data word for each pixel. It
should be noted that each line within the panel includes 1365
pixels, and the intensity of each pixel is represented by 16 data
bits.
[0007] In order to satisfy this requirement, the frame memory
includes a 128 Mbit synchronous dynamic random access memory with
four 32 Mbit banks #1 to #4. The banks #1 and #2 are used for
storing image data of odd-numbered frames, while the banks #3 and
#3 are used for storing image data of even-numbered frames. Each of
the banks #1 to #4 is organized as 4,096 rows by 256 columns by 32
bits. This means that each row within the banks has a capacity for
storing sub-field data of two lines of pixels, and storing a
complete set of sub-field data for a frame requires 192 rows in
each of the two banks associated with the frame. Each banks
includes 16 regions, which are respectively associated with 16
sub-fields. The row addresses over 3072 are not in use for the WXGA
specification.
[0008] Write and read operations of the frame memory usually adopt
different access sequences. The write operation into the frame
memory is implemented in units of pixel lines, while the read
operation is implemented in units of sub-fields. For the frame
memory shown in FIGS. 2A through 2D, for example, the write
operation begins with a sequential write of sub-field data of the
1st line for 1st through 16th sub-fields in the order of the
sub-field number. A sequential write of sub-field data of the 2nd
line then follows, a sequential write of sub-field data of the 3rd
line then follows, and so force, until a sequential write of
sub-field data of the 768th line is completed. The read operation,
on the other hand, begins with a sequential read of sub-field data
of the 1st through 768th lines for the 1st sub-field. A sequential
read for the 2nd sub-field then follows, a sequential read for the
3rd sub-field then follows, and so force, until the sequential read
for the 16th sub-fields is completed.
[0009] FIG. 3 shows an exemplary access sequence of the frame
memory shown in FIGS. 2A through 2D. FIG. 3 refers to symbols "Rd"
and "Wr" as read and write operations of sub-field data of a
certain line for a certain sub-field, respectively. Write sub-field
data 902 of the 1st line for the 1st through 16th sub-fields are
serially inputted to the frame memory in synchronization with a
write horizontal sync signal 901, while read sub-field data 904 of
the 1st through 16th lines for the 1st sub-fields are serially
outputted from the frame memory in synchronization with a read
horizontal sync signal 903. The read and write operations for the
read and write sub-field data are alternately performed in
synchronization with the read horizontal sync signal 903.
[0010] The access sequence shown in FIG. 3 has an advantage that it
requires only a single port for a frame memory to exchange write
and read sub-field data, that is, eliminates necessity for
providing separated write and read ports within a frame memory.
This advantageously reduces cost of frame memories.
[0011] Another advantage of the access sequence is its simplicity,
and this feature ensures write and read operations of sub-field
data for a given frame in the associated frame time.
[0012] Display drivers are desirably designed to allow the numbers
of sub-fields of write and read image data to be independently
adjustable, because this promotes the use of the same display
driver for driving different display panels, and thereby reduces
cost of display drivers through a mass production effect. This
requirement has been enhanced by an increase in the number of
sub-fields within a frame for improving image quality.
[0013] In addition, display drivers are desirably designed to
achieve fast write operation to frame memories integrated therein.
The aforementioned method and system suffer from a drawback that
the write cycle time is restricted by the read cycle time, which is
determined by the frame rate or the frame time.
3. PRIOR ART DOCUMENTS
[0014] Japanese Unexamined Patent Application No. Jp-A 2001-215934
discloses a display driver for allowing users to select a desired
image from among inputted images and to quickly switch images
without causing deterioration of the images.
[0015] Japanese Unexamined Patent Application No. Ja-A-Heisei
10-260677 discloses a technique for allowing a display driver
adopting a double buffer architecture to display a static image on
the display screen without using special controller circuit. The
display driver includes a pair of frame memories and a switching
circuitry to achieve a double buffer technique. For displaying a
static memory, the display driver disables the switching circuitry
and reads out the same image data from selected one of the frame
memories.
[0016] Japanese Unexamined Patent Application No. Jp-A-Heisei
10-268833 discloses a method and system for achieving fine
resolution and gray scale without using a high speed frame memory.
The method and system rearranges a bit frame in response to pixel
positions and firing timings, and stores the rearranged bit frame
into a plurality of frame memories so that the system are allowed
to obtain the bit frame at a single read cycle. This effectively
eliminates the necessity for using a high speed memory device as
the frame memory.
[0017] Japanese Unexamined Patent Application No. Jp-A-Heisei
11-175024 discloses a plasma display system for achieving fine
resolution and gray scale without using a high speed frame memory.
Bit frames are allocated and stored into a frame memory in response
to the positions of pixels associated therewith, and a dual port
memory is used as the frame memory. This allows the frame memory to
provide address drivers with address data without reordering. This
effectively eliminates the necessity for using a high speed memory
device as the frame memory.
[0018] Japanese Unexamined Patent Application No. Jp-A Heisei
8-194451 discloses an LCD (liquid crystal display) driver using a
multi-line selection method (MLS method) for calculating a column
line voltage in a short time with a low-speed DRAM. The disclosed
LCD driver includes a pair of frame memories, one storing
odd-numbered bit frames, and the other storing even-numbered bit
frames. The associated pair of bit frames are successively
transferred to from the frame memory to a column voltage
calculating circuit.
[0019] Japanese Unexamined Patent Application No. Jp-A-Heisei
8-76713 discloses a technique for driving an electroluminescent
display or a liquid crystal displays with a CRT (cathode ray tube)
controller. The technique divides a display screen into a pair of
regions. One of the regions is driven in response to image data
received from a video memory. Image data for the remaining regions
are transferred to associated frame memories, and remaining regions
are driven in response to image data received from the frame
memories.
[0020] Japanese Unexamined Patent Application No. Jp-A-Heisei
5-303477 discloses a display control system for reducing the time
required for reading out data as less as possible while maintaining
the extensibility of the system by previously storing the
arrangement information of addresses for data required for
processing.
SUMMARY OF THE INVENTION
[0021] An object of the present invention is to provide a display
driver designed to allow the numbers of sub-fields of write and
read image data to be independently adjustable.
[0022] Another object of the present invention is to provide a
display driver designed to achieve fast write operation to a frame
memory integrated therein.
[0023] In an aspect of the present invention, a method for
accessing a frame memory integrated within a display panel driver
driving a display panel, the method is composed of:
[0024] serially performing write operations for writing sub-field
data of a pixel line within the display panel for a plurality of
sub-fields into the frame memory; and
[0025] serially performing read operations for reading sub-field
data of a plurality of pixel lines for a sub-field from the frame
memory;
[0026] at least two of the write operations being allowed to be
performed between adjacent two of the read operations. It should be
noted that the sub-field data of a given pixel line for a given
designates data representative of illumination or extinction of
each pixel included in the given pixel line during the given
sub-field.
[0027] The method preferably further including:
[0028] providing first and second horizontal sync signals;
[0029] the write operations for writing the sub-field data of the
pixel line for the plurality of sub-fields being performed during a
single cycle of the first horizontal sync signal; and
[0030] each of the read operations for reading the sub-field data
of the pixel line for each of the plurality of sub-fields being
performed during a single cycle of the second horizontal sync
signal.
[0031] Preferably, in response to activation of the read request
signal, one of the read operations associated with the activation
is performed immediately after the activation of the read request
signal when the frame memory is not engaged in write operation,
while the associated one of the read operations is performed after
completion of associated one of the write operations when the frame
memory is engaged in the associated one of the write
operations.
[0032] In this case, the read request signal is preferably kept
activated until the associated one of the read operations is
initiated.
[0033] Preferably, in response to activation of the write request
signal, one of the write operations associated with the activation
is performed immediately after the activation of the write request
signal when the frame memory is not engaged in read nor write
operation, the associated one of the write operations is performed
after completion of associated one of the read operations when the
frame memory is engaged in the associated one of the read
operations, and the associated one of the write operations is
performed after completion of previous one of the write operations
when the frame memory is engaged in the previous one of the write
operations.
[0034] In this case, the write request signal is preferably kept
activated until the associated one of the write operations is
initiated.
[0035] In another aspect of the present invention, a memory
controller for controlling access to a frame memory is composed of
a timing controller developing read and write start pulse signals
in response to write and read request signals, and a read/write
operation control unit responsive to the read and write start pulse
signals for initiating read operations for reading sub-field data
from the frame memory, and write operations for write sub-field
data into the frame memory. The timing controller develops the read
and write start pulse signals to allow the read/write operation
control unit to initiate at least two of the write operations
between adjacent two of the read operations.
[0036] The timing controller preferably includes a state machine
switching a state of the frame memory among a plurality of states
in response to a reset signal, the write and read request signals,
the plurality of states including an idle state, a write start
state, a first write operation state, and a second write operation
state. The state machine is designed to switch the state of the
frame memory to the idle state in response to activation of the
reset signal, to switch the state of the frame memory to the write
start state in response to first activation of the write request
signal, to unconditionally switch the state of the frame memory to
the first write operation state after placing the frame memory in
the write start state to initiate one of the write operations, and
to switch the state of the frame memory to the second write
operation state in response to second activation of the write
request signal during the one of the write operations to initiate
next one of the write operations.
[0037] When the plurality of states further includes a read start
state, and a read operation state, the state machine is preferably
designed to switch the state of the read start state in response to
activation of the read request signal when the frame memory is
placed in any of the idle state and the first and second write
operation states, and to unconditionally switch the state of the
frame memory to the read operation state after placing the frame
memory in the read start state to initiate one of the read
operations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a diagram illustrating a conventional sub-field
addressing method for achieving a gray scale;
[0039] FIGS. 2A through 2D are memory maps of a conventional frame
memory adapted to the conventional sub-field addressing method;
[0040] FIG. 3 is a timing chart illustrating a conventional method
for accessing a frame memory;
[0041] FIG. 4 is a timing chart illustrating a method for accessing
a frame memory in one embodiment of the present invention;
[0042] FIG. 5 is a block diagram of a memory controller used for
implementing the method in the embodiment;
[0043] FIG. 6 is a timing chart illustrating operation of a timing
controller within the memory controller;
[0044] FIG. 7 is a diagram illustrating state transition of the
frame memory achieved by a state machine within the timing
controller;
[0045] FIGS. 8A through 8I are timing charts illustrating read and
write operations of sub-field data of a certain pixel line for a
certain sub-field, achieved through the state transition
illustrated in FIG. 7;
[0046] FIG. 9 is a timing chart illustrating a process for issuing
commands during a read operation; and
[0047] FIG. 10 is a timing chart illustrating a process for issuing
commands during a write operation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] Preferred embodiments of the present invention are described
below in detail with reference to the attached drawings.
[0049] FIG. 4 shows a procedure of accessing a frame memory in one
embodiment of the present invention. The frame memory interfaces a
signal processor generating desired image data, and a data line
driver driving data lines of a display panel in response to the
image data. The frame memory in this embodiment has the same
structure and map allocation as that described with reference to
FIGS. 2A through 2D. The display panel includes 768 pixel lines in
an direction orthogonal to the data lines to satisfy a WXGA
specification.
[0050] The image data received from the signal processor is
referred to as a write image data 102, and the image data
transmitted to the data driver is referred to as a read image data
104. The write and read image data 102 and 104 include sub-field
data of each pixel line for each sub-field, each of which is
represented by a hexagon in FIG. 4. The sub-field data within the
write image data 102 may be referred to as write sub-field data,
while the sub-field data within the read image data 104 may be
referred to as read sub-field data.
[0051] The frame memory receives a pair of horizontal sync signals
from the signal processor and the display panel, and the one from
the signal processor is referred to as a write horizontal sync
signal 101, and the other is referred to as a read horizontal sync
signal 103. Write operation of the write image data 102 into the
frame memory is synchronous with the write horizontal sync signal
101. The cycle of the write horizontal sync signal 101 is
determined by the frame time and the number of pixel lines of the
display panel.
[0052] The write operation of the write sub-field data is achieved
in unit of pixel lines. In detail, sub-field data of the 1st pixel
line for the 1st through 16th sub-fields are serially inputted to
the frame memory, and a serial write operation of the sub-field
data of the 2nd pixel line for the 1st through 16th sub-fields then
follows. The same goes for the remaining pixel lines, until the
write operation of sub-field data of the 768th pixel line is
completed.
[0053] By contrast, the read operation of the read image data 104
is achieved in unit of sub-fields. Sub-field data of the 1st to
768th pixel lines for the 1st sub-field are serially outputted from
the frame memory, and a serial read operation of the sub-field data
for the 2nd sub-field then follows, and so force, until the
sub-field data for the 14th sub-field is completed. The read
operation of sub-field data is performed in response to the
activation of the read horizontal sync signal 103.
[0054] In this embodiment, the signal processor establishes 16
sub-fields within a frame, while the data line driver establishes
14 sub-fields within a frame. In other words, the write image data
102 includes 16 sub-field data for one frame, while the read image
data 104 includes 14 sub-fields data for the frame. The difference
in the number of the sub-fields requires the frame memory to
receive from the signal processor sub-field data more than those
outputted to the data line driver in each frame.
[0055] In order to achieve this requirement, the access sequence is
adapted to perform write operation of write sub-field data for one
or more sub-fields between read operations adjacent in time in
response to the length of idle time therebetween, as indicated by
symbols "Rd", "Wr(1)", and "Wr(2)" in FIG. 4, where the symbols
"Rd" represent the read operations while the symbols "Wr(1)", and
"Wr(2)" represent the write operations. In the event that the read
horizontal sync signal 103 is activated during a write operation, a
read operation is initiated after the completion of the write
operation.
[0056] FIG. 5 shows a block diagram of a memory controller 1 for
implementing the access sequence in this embodiment. The memory
controller 1 is adapted to control accesses to the frame memory,
which is denoted by a numeral "2" in FIG. 5. The memory controller
1 is composed of a timing controller 10, a write operation
controller 20, a read operation controller 30, and a selector
40.
[0057] The timing controller 10 is responsive to a write request
signal 203 from the signal processor (not shown), a read request
signal 204 from the data line driver (not shown), and a reset
signal 201 for developing write start pulse signal 206 and read
start pulse signal 205. The write start pulse signal 206 determines
the respective timings when write operations are performed, while
the read start pulse signal 205 determines the timings when read
operations are performed. The write request signal 203 is
synchronous with the write horizontal sync signal 101, while the
read request signal 204 is synchronous with the read horizontal
sync signal 102.
[0058] Referring back to FIG. 5, the timing controller 10 includes
a write counter 11, a read counter 12, and a state machine 13. The
write counter 11 counts clock pulses (not shown) to determine the
timings when the write start pulse signal 206 is activated.
Correspondingly, the read counter 12 counts the clock pulses to
determine the timings when the read start pulse signal 205 is
activated.
[0059] The state machine 13 controls state transition of the frame
memory 2. The state machine 13 places the frame memory 2 in a state
selected from among the group consisting of an idle state "IDLE", a
read start state "RST", a read operation state "READ", a write
start state "WST", first and second write operation states "WRITE1"
and "WRITE2". The state machine 13 is reset in response to the
activation of the reset signal 201 to place the frame memory 2 in
the idle state "IDLE".
[0060] The write and read operation controllers 20, 30, and the
selector 40 function as a control unit responsive to the read and
write start pulse signals 205 and 206 for issuing commands which
indicates the frame memory 2 to initiate read or write operations
of sub-field data.
[0061] In detail, the write operation controller 20 is responsive
to the write start pulse signal 206 for developing write commands.
The write operation controller 20 includes a write counter 21
counting the clock pulses, and the write commands are issued in
response to the number of the counts in the write counter 21.
[0062] The read operation controller 30 is responsive to the read
start pulse signal 205 for developing read commands. The read
operation controller 30 includes a read counter 31 counting the
clock pulses, and the read commands are issued in response to the
number of the counts in the read counter 21.
[0063] The write and read counters 21, and 31 are operated so that
the numbers of the counts therein are respectively identical to
those in the write and read counters 11, and 12 within the timing
controller 10.
[0064] The selector 40 selects the write and read commands received
from the write and read operation controllers 20 and 30. The
selected commands are provided for the frame memory 2.
[0065] FIG. 6 illustrates a timing chart of the operation of the
memory controller 1.
[0066] The signal processor and the data line driver activate the
write and read request signals 203, and 204 in synchronization with
the write and read horizontal sync signals 201, and 202,
respectively.
[0067] In response to the activation of the read request signal
204, the timing controller 10 determines whether the frame memory 2
is engaged in write or read operations. If not, the timing
controller 10 activates the read start pulse signal 205 to initiate
read operation. Otherwise, the timing controller 10 ignores the
read request signal 204. This results in that the read request
signal 204 is kept activated.
[0068] On the other hand, in response to the activation of the
write request signal 203, the timing controller 10 determines
whether frame memory 2 is engaged in write or read operations. If
not, the timing controller 10 activates the write start pulse
signal 205 to initiate write operation. Otherwise, the timing
controller 1-ignores the write request signal 203. This results in
that the write request signal 203 is kept activated.
[0069] The timing controller 10 is allowed to activate the read
start pulse signal 205 once and to activate the write start pulse
signal 205 once or twice, during a single cycle of the read
horizontal sync signal 202. In an alternative embodiment, the
timing controller 10 may be allowed to activate the write start
pulse signal 205 three times or more.
[0070] Consequently, the timing controller 10 allows the frame
memory 2 to perform one or more write operations in response to the
activation of the write start pulse signal 205 between the adjacent
read operations.
[0071] The operation of FIG. 6 is achieved through the state
transition control by the state machine 13. FIG. 7 shows a state
transition diagram of the frame memory 2. As described before, the
frame memory 2 is allowed to be placed in the idle state "IDLE",
the read start state "RST", the read operation state "READ", the
write start state "WST", the first and second write operation
states "WRITE1" and "WRITE2".
[0072] Activation of the reset signal 201 resets the state machine
13 to place the frame memory 2 in the idle state "IDLE".
[0073] In response to the read request, that is, the activation of
the read request signal 204, the state of the frame memory 2 is
switched to the read start state "RST" to initiate read operation.
The state of the frame memory 2 is then unconditionally switched to
the read operation state "READ" to perform read operation.
[0074] If the write request is not issued during the read
operation, that is, if the write request signal 203 is kept
deactivated, the state of the frame memory 2 is switched to the
idle state "IDLE" in response to the completion of the read
operation. If the write request is issued during the read
operation, the state of the frame memory 2 is switched to the write
start state "WST" to initiate the first write operation.
[0075] The state of the frame memory 2 is then unconditionally
switched from the write start state "WST" to the first write
operation state "WRITE1". After the completion of the first write
operation, the state of the frame memory 2 is then switched to any
of the states "IDLE", "WST", and "WRITE2" in response to the issue
of the write and read requests. If none of the requests is issued,
the state of the frame memory 2 is switched to the idle state
"IDLE" in response to the completion of the first write operation.
If the read request is issued during the first write operation, the
state of the frame memory 2 is switched to the read start state
"RST" to initiate read operation. If the write request is issued
without the read request issued, the state of the frame memory 2 is
switched to the second write state "WRITE2" to initiate second
write operation.
[0076] After the completion of the second write operation, the
state of the frame memory 2 is then switched to any of the states
"IDLE", "WST", and "RST". If the second write operation is
completed without the read and write requests issued, the state of
the frame memory 2 is switched to the idle state "IDLE". If the
read request is issued during the second write operation, the state
of the frame memory 2 is switched to the read start state "RST" to
initiate read operation. If the write request is issued during the
second write operation without the read request issued, the state
of the frame memory 2 is switched to the write start state "WST" to
initiate first write operation.
[0077] FIGS. 8A through 8I are timing charts illustrating read and
write operations of sub-field data of a certain pixel line for a
certain sub-field, achieved through the state transition
illustrated in FIG. 7. The state transition achieves selected one
of the following operations: a "discrete" read operation shown in
FIG. 8B, a "discrete" write operation shown in FIG. 8C, a write
operation after a read operation shown in FIG. 8E, a read operation
after a first write operation shown in FIG. 8F, a second write
operation after a first write operation shown in FIG. 8H, and a
read operation after a second write operation shown in FIG. 8I. The
"discrete" read operation designates a read operation after which
the state of the frame memory 2 is switched to the idle state
"IDLE", while the "discrete" write operation designates a write
operation after which the state of the frame memory 2 is switched
to the idle state "IDLE".
[0078] Referring to FIG. 8B, the "discrete" read operation is
initiated in response to the activation of the read request signal
204 with the write request signal 203 deactivated. In response to
the activation of the read request signal 204, that is, the issue
of the read request, the state of the frame memory 2 is switched to
the read start state "RST". This allows the read start pulse signal
205 to be activated, and the read counter 12 to start counting the
clock pulses. In response to the read start pulse signal 205 being
activated, the state of the frame memory 2 is switched to the read
operation state "READ". This allows the read operation to be
performed to achieve read-out of sub-field data of a target pixel
line for a target sub-field, which includes 4096 (=64.times.64)
data bits, to be read out from the frame memory 2, which includes a
64-bit output port, while the read counter 12 counts 64 clock
pulses denoted by numbers 0 to 63 in FIG. 8B. The frame memory 2
then prepares a following access while the read counter 12 counts
the following four "dummy" clock pulses denoted by numbers 64 to
67. Those skilled in the art would appreciate that the number of
the dummy clock pulses may be changed.
[0079] In response to none of read and write request being
additionally issued before the completion of the read operation,
the state of the frame memory 2 is switched back to the idle state
"IDLE", and the "discrete" read operation is completed.
[0080] Referring to FIG. 8C, the "discrete" write operation is
initiated in response to the activation of the write request signal
203 with the read request signal 204 deactivated. In response to
the activation of the write request signal 203, that is, the issue
of the write request, the state of the frame memory 2 is switched
to the write start state "WST". This allows the write start pulse
signal 20 to be activated, and the write counter 11 to start
counting the clock pulses. In response to the write start pulse
signal 205 being activated, the state of the frame memory 2 is
switched to the first write operation state "WRITE1", and this
allows sub-field data of a target pixel line for a target sub-field
to be written into the frame memory 2 while the write counter 12
counts 64 clock pulses denoted by numbers 0 to 63 in FIG. 8C. The
frame memory 2 then prepares the following access while the write
counter 11 counts the following ten "dummy" clock pulses denoted by
numbers 64 to 73.
[0081] In response to none of read and write request being
additionally issued before the completion of the write operation,
the state of the frame memory 2 is switched back to the idle state
"IDLE", and the "discrete" write operation is completed.
[0082] Referring to FIG. 8E, the write operation after the read
operation is initiated in response to the activation of the write
request signal 203 during the read operation. The read operation is
performed while the read counter 12 counts 68 clock pulses, denoted
by numbers 0 through 68 in FIG. 8E. In response to the completion
of the read operation with the write request signal 203 activated,
the state of the frame memory 2 is switched to the write start
state "WST". This allows the write start pulse 205 to be activated
to switch the state of the frame memory 2 to the first write
operation state "WRITE1". The write operation is then performed
without the state of the frame memory 2 switched to the idle state
"IDLE".
[0083] Referring to FIG. 8F, the read operation after the first
write operation is initiated in response to the activation of the
read request signal 204 during the first write operation. The write
operation is performed while the write counter 11 counts 67 clock
pulses, denoted by numbers 0 through 66 in FIG. 8F. In response to
the completion of the write operation with the read request signal
204 activated, the state of the frame memory 2 is switched to the
read start state "RST". This allows the read start pulse 206 to be
activated to switch the state of the frame memory 2 to the read
operation state "READ". The read operation is then performed
without the state of the frame memory 2 switched to the idle state
"IDLE".
[0084] Referring to FIG. 8H, the second write operation after the
first write operation is initiated in response to the activation of
the write request signal 203 during the first write operation. The
write operation is performed while the write counter 11 counts 67
clock pulses, denoted by numbers 0 through 66 in FIG. 8H. In
response to the completion of the first write operation with the
write request signal 203 activated, the state of the frame memory 2
is switched to the second write operation state "WRITE2". This
state transition allows the second write operation to be
successively performed without the state of the frame memory 2
switched to the idle state "IDLE".
[0085] When another write operation is issued during the second
write operation, the state of the frame memory 2 is switched to the
write start state "WST" in response to the completion of the second
write operation. This allows the write start pulse signal 206 to be
activated to place the frame memory 2 in the first write operation
state "WRITE1", and the following requested write operation is then
performed. It should be noted the state of the frame memory 2 is
not switched to the idle state "IDLE" during this state transition.
The direct state transition from the state "WRITE2" to the state
"WST" effectively reduces the overhead during the write
operation.
[0086] Referring to FIG. 8I, the read operation after the second
write operation is initiated in response to the activation of the
read request signal 204 during the second write operation. The
second write operation is performed while the write counter 11
counts 68 clock pulses. The read request issued during the second
write operation is ignored before the second write operation is
completed. In response to the completion of the second write
operation with the read request signal 204 activated, the state of
the frame memory 2 is switched to the read start state "RST". This
state transition allows the read write operation to be successively
performed without the state of the frame memory 2 switched to the
idle state "IDLE".
[0087] FIG. 9 is a timing chart illustrating a process for issuing
commands during the read operation. The issue of the commands is
synchronous with the clock pulses. In response to the activation of
the read start pulse signal 205, the read counter 31 within the
read operation controller 30 starts counting the clock pulses. The
read counter 31 counts 64 clock pulses until sub-field data of a
target line for a target sub-field is completed. A decoder (not
shown) within the read operation controller 30 decodes the number
of the counts in the read counter 31 to develop the commands 605.
The commands 605 typically includes a bank active command (ACT
command) and the following read commands (RD commands).
[0088] FIG. 9 is a timing chart illustrating a process for issuing
commands during the read operation. The issue of the commands is
synchronous with the clock pulses. In response to the activation of
the read start pulse signal 205, the read counter 31 within the
read operation controller 30 starts counting the clock pulses. The
read counter 31 counts 64 clock pulses until data read of sub-field
data of a target line for a target sub-field is completed. A
decoder (not shown) within the read operation controller 30 decodes
the number of the counts in the read counter 31 to develop the
commands typically including a bank active command (ACT command)
and the following read commands (RD commands).
[0089] FIG. 10 is a timing chart illustrating a process for issuing
commands during the write operation. The issue of the commands is
synchronous with the clock pulses. In response to the activation of
the write start pulse signal 206, the write counter 21 within the
write operation controller 20 starts counting the clock pulses. The
write counter 31 counts 64 clock pulses until data write of
sub-field data of a target line for a target sub-field is
completed. A decoder (not shown) within the write operation
controller 20 decodes the number of the counts in the write counter
21 to develop the commands, typically including, for the target
bank, a bank active command (ACT command) and the following write
commands (RD commands), and for the remaining banks, a refresh
command (REF command), and a precharge command (PHG command).
[0090] In conclusion, the system and method for accessing the frame
memory in this embodiment allows the numbers of sub-fields of write
and read image data to be independently adjustable, because the
frame memory access method is designed to allow one or more write
operations to be performed between the adjacent read operations
under the control of the state machine 13. This effectively
achieves fast write operation to a frame memory through making use
of idle time between the adjacent read operations.
[0091] Although the invention has been described in its preferred
form with a certain degree of particularity, it is understood that
the present disclosure of the preferred form has been changed in
the details of construction and the combination and arrangement of
parts may be resorted to without departing from the scope of the
invention as hereinafter claimed.
* * * * *